Whistler observation at Okinawa, Japan during the IMS

Observations of low-latitude whistlers were conducted at Okinawa (geomagnetic lat 15.3 N) a subtropical region with no clear seasonal variations in whistler dispersion. The average diurnal variation of whistler dispersions varies from 20 root s in the evening to 9 root s at dawn. The occurence frequency of whistlers peaks in the winter night and has no evening peak. Whistler dispersions fit well computed ones along the International Geomagnetic Reference Field line passing through Okinawa. The correlation coefficient between whistler dispersions and F0F2 at Okinawa is 0.76 for the winter months. Whistler activity is sporadic and increases with increasing local geomagnetic activity. Results of whistler direction finding show that arrival directions of whistlers lie within 30 deg off the local zenith in the south-east. Observations support the ducted propagation of low-latitude whistlers.